PREPARE cake mix as directed on package for 2 (8-inch or 9-inch) round cake layers. Cool completely.
Pour milk into medium bowl. Add pudding mixes. Beat with wire whisk 2 minutes. Immediately spread over tops of cake layers.
Place 1 cake layer on top of the other. Frost top and sides of cake with whipped topping. Refrigerate until ready to serve. Garnish with lemon slices and fresh mint leaves.